The present invention relates to a copier, printer, facsimile apparatus or similar color or color/black-and-white electrophotoraphic image forming equipment and, more particularly, to a rotary developing device incorporated in such equipment and having a plurality of developing units around a common rotary shaft.
Conventional color image forming equipment include a full color copier which exposes an image carrier imagewise by light components of different colors, develops the resulting latent images by toners each being complementary in color to associated one of the light color components, and transfers the resulting toner images one above another to a single paper sheet. Multicolor image forming equipment is also conventional which exposes a plurality of image carriers by respective images to be reproduced in different colors, develops the resulting latent images by developers of different colors, and transfers the resulting toner images one above another to a single paper sheet. While such equipment needs a plurality of developing units, constructing the individual developing units independently of one another and arranging them around the image carrier increases the overall size of the equipment.
In light of the above, there has been developed a rotary developing device having a rotatable body or revolver located in the vicinity of an image carrier, and a plurality of developing units mounted on the outer periphery of the revolver and located at predetermined positions. The revolver is rotated to sequentially bring the developing units to a developing position, thereby developing each latent image formed on the image carrier in a particular color. In such a rotary or revolver type developing device, when any one of the developing units is brought to the developing position, a developer carrier incorporated in the developing unit has to be driven in a rotary motion. For this purpose, it is a common practice to mount a developing gear on each image carrier and drive it by a drive gear which is connected to an external drive source. However, when the developing gears are driven by respective drive gears, the structure becomes complicated and bulky. To reduce the size of this type of developing device, various drive mechanisms have been proposed in the past, e.g., Japanese Patent Laid-Open Publication Nos. 172660/1983 and 99169/1986 and Japanese Utility Mode Laid-Open Publication No. 110442/1977. The conventional drive mechanisms, however, have various problems left unsolved. Specifically, the gears are apt to hit against each other to have the teeth thereof broken or to fail to mesh accurately with each other. With the conventional mechanisms, it is impossible to set up and interrupt the meshing of the gears, as desired. In addition, the gears are likely to produce noise due to vibration.